The present invention relates to the industrial cleaning of stop log slots, sometimes referred to as stop log guides, by removing and flushing away both attached and loose debris such as marine life silt from the stop log seating surfaces using a frame and attachments without the need of human divers. Stop logs are commonly used in industrial applications such as power plant intake cavities, canals, and discharge conduits, tunnels and piping to provide a barrier or dam to allow water to drained or pumped out of an area or structure that is otherwise flooded. The areas or structures are normally drained for the purpose of allowing workers to enter the space and perform maintenance activities that either can not or are not cost effective to perform underwater. The stop log is basically a temporary wall that is lowered into a slot or guides that are embedded into a concrete structure sealing on the bottom and the edges on the side facing the space to be drained or pumped out acting as a dam. The guides/slots are commonly formed by two steel C-channels or a steel plate forming a shape similar to a C-channel with the open sides facing each other, with a smooth flat sealing surface at the bottom running between the channels, and open at the top end of each channel to allow the stop log to be inserted. The seals act as a gasket sealing against the seating/sealing surface of the embedded guides. When the water is pumped out of the space on one side of the stop log the differential pressure caused by water on the other side of the stop log compresses the seals sealing water out.
It is important that the seating surfaces be as clean and flat as possible to prevent leakage past the stop log seals and prevent damage to the seals during stop log installation. Marine life such as barnacles, shell fish and other debris trapped under seals can create a leak path by creating a rough seating surface or cutting or tearing the seal material. The traditional of cleaning the seating or sealing surfaces is to use divers with various handheld tools and machines that scrape, cut or scrub off attached marine life or debris which is then either flushed away with a hand held vacuum, water hose, water canon, or just manually pushed away from the seating surfaces.
The use of divers although effective is inherently dangerous, time consuming and expensive. The cleaning of stop log slots/guides also constitutes a confined space dive further increasing risk and legal requirements. The typical cost of a dive team exceeds $1,500 a day. This does not include the typical dive support including plant safety tagging to make the dive location safe, possible security depending on the facility, and other support functions that frequently accompany dive activities which can exceed the cost of the dive team. A typical stop log slot cleaning operation can require up to nine workers and can take eight hours. In spite of industrial safety regulations dive accidents continue to occur on a regular basis and do claim lives.
In addition the dive activity to clean stop log slots requires the system to be shut down to prevent the diver from being drawn into operating pumps and equipment. There is increasing pressure to reduce down time in the deregulated electric utility and other industry to remain competitive. Shortcuts or mistakes in this area occur too often and can have fatal consequences.
A typical stop log cleaning activity involves obtaining safety tag-out isolating the system to make the dive location safe, processing a truck load of dive equipment through security, setting up and dive equipment, a pre-dive job brief, the dive to clean the stop log slots, and break-down and reloading dive equipment at the end of the job.
Dive cleaning is done most commonly with a handheld scraper tool similar to a putty knife followed by a flush of the bottom with water or air pressure. The diver is suspended or floating in water and while he scrapes or cuts the attached marine life from the seating surface of the slot, making the job more difficult and time consuming. The diver force that is applied in scraping is also limited by the physical strength and endurance of the diver. Visibility for the diver is commonly low in this environment and gets worse during the cleaning operation due to stirring up silt and mud.
There are other tools available to divers to clean surfaces including hand held hydrolazers (higher pressure versions of pressure washers), handheld air powered or hydraulic powered rotating brushes that may include a vacuum attachment that removes debris that is removed by the brushes from the area. Although these tools can be effective, the supporting equipment is expensive, they are operated by divers, and can be a hazard to the diver himself. Hydrolazers require extreme caution and protective gear since the high pressure water jet can cut or inject into the diver and injure or kill them. Operating a hydrolazer while suspended in water adds to the risk. The risk of a rotating brush with a divers air lines floating in the area should be obvious. There is also the possible risk to the diver from sharks, barracuda, alligators etc. (depending on the job location) that may become interested in the food being stirred up by the cleaning operation.